Multi-site (or “wide area”) communication systems provide wide-area coverage for users (also referred to herein as “subscribers) of the system. These systems comprise a number of sites (or radio frequency (RF) sites), with each site corresponding to a different geographic coverage area and each site having located therein an infrastructure device (also referred to herein as a “repeater”) serving the coverage area by managing one or more channels in the coverage area. Accordingly, for purposes of the teachings herein, a site is characterized by a repeater that serves a particular coverage area and a channel for wireless communication device transmissions. Some or all of the infrastructure devices in a multi-site communication system may be networked or connected together via a backend network to provide the wide-area coverage via one or more logical wide-area channels, and in many instances two or more of the coverage areas have some degree of overlap.
Multi-site communication systems may be designed as trunked systems or conventional systems. In trunked systems, a limited number of communication channels are shared among a much larger number of subscribers to facilitate efficient use of the system's communication resources. Thus, to afford each subscriber a reasonable opportunity to use the system's resources, one or more control channels are utilized by the infrastructure to allocate and switch the shared resources between the many subscribers in the system. In general, when a subscriber wants to communicate on the trunked system, he or she sends a request via a wireless communication unit (hereinafter referred to as a “subscriber unit”) on the control channel to communicate with another subscriber or group of subscribers (also referred to herein as a “talkgroup”) on their subscriber units. In turn, the requesting subscriber unit (and the subscriber units to which it attempts to communicate) receives back on the control channel the allocation of a traffic channel to use for communicating. Upon the conclusion of the communication, the allocated channel is released for use by other subscriber units in the system.
In conventional systems, a number of communication channels are also shared amongst a number of subscribers (although the number of subscribers per channel is typically much smaller than in trunked systems). However, there is no control or switching mechanism provisioned in the infrastructure to allocate the resources among the subscribers in the system. Thus, in contrast to a trunked system, each channel in a conventional system is dedicated to one or more talkgroups enabling the subscriber members of each assigned talkgroup to control access to the channel through their subscriber units by manually selecting the channel or selecting the talkgroup that is assigned to the channel in order to start a communication session and transmit and receive media during the session.
A subscriber of a talkgroup in a conventional communication system is required, before talking on their subscriber unit, to determine whether another subscriber is already talking on the current communication channel allocated to that talkgroup for use. If the channel is busy or already in use, the subscriber must wait until the channel is available in order to make a call. Existing conventional communication systems rely on the fact that, generally, all of the subscribers in a talkgroup are served by the same communication channel at the same site. Namely, when all the subscribers of a talkgroup are served at the same RF site, determining the availability of the communication channel is relatively simple. Because all individual subscribers of a talkgroup are sharing the same communication channel, the subscribers can simply listen to the communication channel on their communication or subscriber unit(s) to detect whether or not the channel is currently being used by another. When a first subscriber unit detects activity on the communication channel, the first subscriber unit indicates this as appropriate to the first subscriber. The first subscriber, therefore, knows that the channel is busy. The conventional communication network infrastructure is not required to do anything special to determine or indicate that the channel is busy because the presence of audio transmissions is sufficient indication to the subscribers.
If no other subscriber is currently actively using the communication channel, then the subscriber can begin audio, knowing that other subscribers of the same talkgroup on their communication channel will be able to hear the audio when it is repeated by the channel's base repeater or RF site. This works for communication subscribers who all share a single channel at a single RF site. Unfortunately, subscribers who are not served at the same RF site are not aware of when the communication channel ascribed to their talkgroup in a different RF site is busy.
Talkgroup subscribers may not all be served by a single base repeater or RF site, as in the case of a communication network having multiple channels spread across multiple RF sites which are interconnected to form a conventional wide area communication network. Such a network gives rise to the problem of a talkgroup having subscribers spanning more than one channel (i.e., subscribers present at more than one RF site). The talkgroup subscribers at one channel (RF site) have no way of knowing whether or not the communication channels used by their talkgroup at other RF sites are already in use. While the talkgroup's communication channel at the subscriber's own RF site may be available, the talkgroup's communication channel at one or more of their talkgroup's other RF sites may already be in use by other subscribers or talkgroups. If a first subscriber at a first RF site begins to talk, members of their talkgroup at the first RF site will hear the audio, but members of their talkgroup at other RF sites where the talkgroup's channel is already in use by other subscribers will not hear the first subscriber's audio.
Accordingly, there is a need for a method to alert subscribers about activity on the communication channels allocated to their talkgroup at other sites within a conventional wide area communication system.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help improve understanding of various embodiments. In addition, the description and drawings do not necessarily require the order illustrated. It will be further appreciated that certain actions and/or steps may be described or depicted in a particular order of occurrence while those skilled in the art will understand that such specificity with respect to sequence is not actually required. Apparatus and method components have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the various embodiments so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein. Thus, it will be appreciated that for simplicity and clarity of illustration, common and well-understood elements that are useful or necessary in a commercially feasible embodiment may not be depicted in order to facilitate a less obstructed view of these various embodiments.